1. Field of the Invention
The electrochemical amperometric detection of redox gases such as oxygen is a well established technique, and the electrode used in such a technique is often referred to as a "Clark Electrode". In the case of an oxygen Clark Electrode, this detection is based on oxygen transport through a gas-permeable membrane to an enclosed electrolyte solution, and the subsequent reduction of oxygen dissolved in this solution, usually on a platinum or gold sensing electrode. The potential of this sensing electrode is held at negative potential compared to the potential of the electrolyte solution by use of a reference electrode, classically a silver/silver chloride electrode. A schematic diagram illustrating this conventional approach is shown in FIG. 1 of the accompanying drawings.
The response time of classical detection devices, where the sensing electrode, on which the electrochemical reaction takes place, is separated from the gas-permeable membrane by a thin (e.g. a submillimeter thick) layer of electrolyte solution, is more than 100 seconds. The response time is limited by the linear diffusion rate of the redox gas through the gas-permeable membrane and into the electrolyte solution as depicted in FIG. 1.
The present invention is based on the use of gas-permeable polymer films (for example films a few microns thick of e.g. polypropylene or polyester) metallized on one side (e.g. with gold or platinum). Such metallized films are commercially available and are currently used in the food packaging industry.
At the heart of the present invention is the use of a novel type of composite gas-permeable membrane which has been manufactured by demetallizing (e.g. by using UV excimer laser photoablation) areas of a metallized polymer film, to obtain a regular array of gas-permeable micropores each having a diameter or width of a few microns. The micropores can be in the form of microdiscs and/or microbands, since the shape of each area is of secondary importance.
2. Description of the Related Art
Our prior International application published as WO 9108474 discloses the use of photoablation for the creation of apertures in electrically insulating material when creating microelectrodes and EP-A-0494382 discloses the creation of an electrochemical cell in which photoablation is used to drill holes in an insulating substrate of the cell and to expose metallized areas on the substrate. EP-A-0494382 does disclose a gas-permeable membrane but not one subjected to subsequent thinning (e.g. by photoablation).